Fuel injection valve

ABSTRACT

A fuel injection valve has downstream a valve seat (23), an injector plate (23), which is characterized by having a plurality of swirl-producing elements on the intake side, followed by at least one uninterrupted annular gap in the downstream direction. The swirl-producing elements are arranged in a turbine vane-shaped form by each individual element running mostly radially and being tilted in the peripheral direction and the elements being arranged behind one another in a circular shape. The annular gap (45) represents the spray geometry. With this arrangement the fuel can be finely atomized without additional power consumption. The breakup into minute droplets results in further reduction of the exhaust emissions of an internal combustion engine and in lower if fuel consumption. The fuel injection valve is especially well-suited for use in injection systems of mixture-compression externally ignited internal combustion engines.

FIELD OF THE INVENTION

The present invention relates to a fuel injection valve, and inparticular to a fuel injection valve for a fuel injection system of amixture-compressing externally ignited combustion engine.

BACKGROUND INFORMATION

It is known from German Offenlegungsschrift 2,723,280 to arrange, on afuel injection valve, a fuel breakup element in the form of a flat thindisk having a plurality of narrow curved slots, in the downstreamdirection from a metering orifice. The curved slots produced by etchingin the disk, with their geometry, i.e., their radial width and curvelength, are responsible for the formation of a fuel mist that is brokenup into small droplets. The curved slots arranged in groups divide thefuel according to their geometry in the horizontal plane. The individualslot groups must be produced very precisely in relation to one anotherin order to achieve the breakup of the fuel in the desired manner. Thecurved slots have a constant opening width over the entire axialextension of the breakup element. Therefore, atomizing can only improvedby varying the horizontal geometry in the radial direction of the slotsin the plane of the breakup element. The fuel is atomized fully anduniformly due to the slots being arranged in groups.

ADVANTAGES OF THE INVENTION

The fuel injection valve according to the present invention has theadvantage over the related art that high-quality and uniform fineatomization of the fuel is achieved without additional powerconsumption. This is accomplished by the injector plate provided on thefuel injection valve having at least one uninterrupted annular gap sothat the swirling fuel to be sprayed forms a continuous annular jetlamella immediately downstream from the annular gap. Due to the geometryof the injector plate and the annular gap, this lamella has the shape ofa truncated cone or a bell. Because of its surface tension, the fuelcone becomes thinner in its fuel film thickness in the downstreamdirection, i.e. with the increasing diameter, until it breaks up intominute droplets. These minute droplets have a reduced Sauter MainDiameter (SMD) compared to the related art, i.e., a smaller mean dropletdiameter of the sprayed fuel; an SMD of <60 μm can be achieved. As aresult, the exhaust emissions of an internal combustion engine and fuelconsumption can be further reduced among other things.

As an additional advantage, the arrangement according to the presentinvention achieves a uniform distribution of the sprayed fuel on arelatively large surface. This yields a smaller droplet packing densityin the fuel spray formed after the broken-up lamellas and good mixturewith the air intake stream of the internal combustion engine. Inaddition, the danger of droplet coagulation, i.e., recombination intolarger droplets, is reduced.

The possibility of influencing the lamella angle by changing the axialannular gap height represents an additional advantage of the fuelinjection valve according to the present invention. Variation of theannular gap height results, however, in negligible changes in the flowrate, since the stream separates on one side in the annular gap.Therefore the flow rate over the width of the annular gap and thelamella angle over the height of the annular gap can be adjustedseparately.

Due to the radial offset of the annular gap of the injector plate inrelation to the inlet into the helical depressions provided upstreamfrom the annular gap, an S-shaped flow of the fluid is obtained in theinjector plate. This provides the flow with a radial velocity component,which is not lost even at the exit. The flow is given a turbulenceconducive to atomization by the "S-collision" with the flow deflectors.The flow is also given an advantageous swirl component in addition tothe radial component by the swirl-promoting depressions that do not runin a completely radial direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a partial view of a fuel injection valve with an injectorplate according to the present invention.

FIG. 2 shows an axial section of a first embodiment of an injector plateaccording to the present invention.

FIG. 3 shows a top view of the injector plate of FIG. 2.

FIG. 4 shows an axial section of a second embodiment of an injectorplace according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The embodiment illustrated in FIG. 1 is a partial view of a valve in theform of an injection valve for fuel injection systems ofmixture-compressing externally ignited internal combustion engines. Theinjection valve has a tubular valve seat support 1 in which alongitudinal orifice 3 is formed concentrically to a longitudinal valveaxis 2. A tubular valve needle 5, connected at its downstream end 6 toan optionally spherical valve closing element 7, provided on itsperiphery with for example five flats 8, is arranged in longitudinalorifice 3.

The injection valve is actuated in the well-known manner, for example,electromagnetically. An electromagnetic circuit with a magnetic coil 10,an armature 11, and a core 12 are used to axially move valve needle 5,thus closing the valve or opening it against the elastic force of forexample a reset spring (not illustrated). Armature 11 is connected tothe end facing away from valve closing element 7 of valve needle 5through a weld produced by laser, for example, and aligned with core 12.

A guide orifice 15 of a valve seat body 16 is used to guide valveclosing element 7 during its axial motion. Valve seat body 16, which maybe cylindrical, is hermetically welded to the end of valve seat support1 facing away from core 12 in longitudinal opening 3 that runsconcentrically to longitudinal valve axis 2. At its lower end 17, facingaway from valve closing element 7, valve seat body 16 is concentricallyand permanently attached to a supporting ring 21, which may have acup-shaped design and is thus in close contact with valve seat body 16.Supporting ring 21 has a shape for example similar to that of thewell-known cup-shaped spray hole disk with a central area of supportingring 21 being provided with a stepped through orifice 22 to accommodatean injector plate 23 according to the invention.

Valve seat body 16 is connected to supporting ring 21, for example,through a hermetical peripheral first weld 25, produced with a laser forexample. With this type of assembly, the danger of undesirabledeformation of supporting ring 21 in its central area with throughorifice 22 and injector plate 23 mounted therein is avoided. Supportingring 21 is furthermore connected to the wall of longitudinal orifice 3in valve seat support 1, for example through a peripheral andhermetically closing second weld 30.

The insertion depth of the valve seat part, consisting of valve seatbody 16, cup-shaped supporting ring 21 and injector plate 23, intolongitudinal orifice 3 determines the length of stroke of valve needle5, since one end position of valve needle 5 when magnetic coil 10 is notenergized is determined by the close contact of valve closing element 7with a valve seat surface 29 of valve seat body 16. The other endposition of valve needle 5, when magnetic coil 10 is energized, isdetermined, for example, by the close-contact of armature 11 with core12. The distance between these two end positions of valve needle 5 istherefore the stroke.

Spherical valve closing element 7 works with truncated cone-shaped valveseat surface 29 of valve seat body 16; valve seat surface 29 is formedin the axial direction between guide orifice 15 and lower face 17 ofvalve seat body 16.

FIG. 2 shows an axial section of injector plate 23 built into aninjection valve. Injector plate 23 is designed as a plane, flat,circular disk. Injector plate 23 is centered in supporting ring 21.Injector plate 23 is fastened to the injection valve and specifically tovalve seat body 16 using, for example, clamping, which is possible dueto the contour of supporting ring 21. Such a fastening as indirectattachment of injector plate 23 to valve seat body 16 has the advantagethat, contrary to processes like welding or soldering, atemperature-related deformation of the fine annular gap geometry iscompletely avoided. The stepped through orifice 22 in supporting ring 21is dimensioned so accurately that it can accommodate injector plate 23very precisely without stresses. Instead of the even outside contour,injector plate 23 can also have an outside contour stepped in the axialdirection. Supporting ring 21 does not represent, however, a necessarycondition for fastening injector plate 23. Since the fastening optionsare not relevant to the invention, here we shall only briefly refer tothe other well-known bonding processes, such as welding, soldering, orgluing. In the assembled state, an upper face 38 of injector plate 23 isin close contact with lower face 17 of valve seat body 16, as the bottomof cup-shaped supporting ring 21.

Flat injector plate 23 has a plurality of swirl-promoting depressions40, open from the fuel intake side, i.e., the upper face 38 and servingas swirl-producing elements. Swirl-promoting depressions 40 are evenlydistributed around a circle in injector plate 23, with only the generalarrangement of the swirl-promoting depressions 40 being circular. Eachswirl-promoting depression 40 has a cross section that may be, forexample, rectangular. The diameter of the circle on which theswirl-promoting depressions 40 are arranged depends mainly on the widthof an outlet orifice 42 in the valve seat body 16, downstream from valveseat surface 29. In order to achieve unimpeded fuel intake in injectorplate 23 and especially in the swirl-promoting depressions,swirl-promoting depressions 40 are designed so that their internalareas, located closest to longitudinal valve axis 2, have a smallereffective diameter than the diameter of exit orifice 42. The flowdirections are schematically indicated through arrows 44 in FIG. 2.Swirl-promoting depressions 40 are not fully radial, but also have aprecisely defined component in the peripheral (circumferential)direction. The design of swirl-promoting depressions 40 is elucidated bythe top view of injector plate 23 in FIG. 3. This shows the turbinevane-like arrangement of the mostly radial swirl-promoting depressions40, which are however tilted in the peripheral direction and run withtheir longitudinal axes along longitudinal valve axis 2.

Downstream from swirl-promoting depressions 40, a narrow annular gap 45,uninterrupted over its circumference, follows as fuel outlet geometry ininjector plate 23. Annular gap 45 runs, for example, with verticallimiting walls, produced cost-effectively using, for exampleelectroforming (MIGA method: Microstructuring, Electroforming,Deforming), which extend to a lower face 46 of injector plate 23. Thecross section surface of annular gap 45 determines the flow rate, withthe annular gap width being usually in the range between 25 μm and 50μm. For a diameter of approximately 5 mm, injector plate 23 has athickness of 0.2 mm to 0.4 mm, with the axial lengths of swirl-promotingdepressions 40 and annular depression (gap) 45 being approximately thesame (equivalent). These magnitudes for the dimensions of injector plate23 and all other dimensions given in the description are intended tofacilitate comprehension and in no way limit the invention.

In the embodiment shown in FIG. 2, annular gap 45 has a larger diameterthan the effective diameter of inlet areas 47 for the fuel inswirl-promoting depressions 40. Inlet areas 47 are understood here asthe orifice areas of swirl-promoting depressions 40, whereswirl-promoting depressions 40 are not covered by valve seat body 16.The diameter of annular gap 45 is therefore greater than the diameter ofoutlet orifice 42 in valve seat body 16. Thus there is a radial offsetof the inlet and outlet of injector plate 23. An additional offset inthe peripheral direction is necessarily obtained from the arrangement ofswirl-promoting depressions 40 through their not exactly radialorientation. Annular gap 45 runs downstream from the outer radial area,but only so far out that the fuel can flow from swirl-promotingdepressions 40 into annular gap 45 without overlapping. In theswirl-promoting depressions, the fuel has a swirl component acquiredthrough the configuration of swirl-promoting depressions 40 as describedabove. The swirl component results in the exiting fluid lamellawidening, making it possible to obtain a desired jet angle, despiteannular gap 45 being perpendicular to injector plate 23.

A jet geometry providing a large surface area in relation to the amountof fuel is the hollow fuel lamella. A large total surface area isequivalent to (achieved by) the breakup of the fuel into as many smalldroplets as possible. In injector plate 23 according to the presentinvention, the lamella is formed with as large a diameter as possiblewhen passing through annular gap 45. In the downstream direction, thelamella becomes thinner, which is enhanced by the increase in thelamella's circumference caused by its bell shape. The bell shape isobtained from a low-pressure core in the central hollow space of thelamella. The swirl component contributes to an enlargement of thelamella circumference, which further increases the free jet surface areaand makes the lamella break up into smaller drops. Furthermore, thespatial packing density of the droplets decreases for larger lamellacross sections, making droplet coagulation in the fuel spray(recombination of droplets into larger drops) less likely. Lamellabreakup starts at a well-defined axial distance from annular gap 45. Thelamella surface area becomes more undulated as the distance to injectorplate 23 increases due to aerodynamic interactions with the gassurrounding the lamella (Taylor effect). The instability in the lamellaincreases with increasing distance from annular gap 45 until a pointwhere it suddenly breaks up into minute fuel droplets. The advantage ofthis arrangement consists of the fact that almost no other disturbancesoccur aside from lamella undulation.

The jet angle of the exiting lamella can be varied and adjusted byengineering measures. The jet angle can be influenced by the followingfactors among others:

the shape of swirl-promoting depressions 40 (radial component toperipheral component ratio),

ratio of the outer diameter of swirl-promoting depressions 40 to thediameter of annular gap 45,

degree of overlap, i.e., size of the overlap of swirl-promotingdepressions 40.

FIG. 4 shows the axial section of a second embodiment of an injectorplate 23, which differs from injector plate 23 of FIGS. 2 and 3 only bythe fact that the S-shaped flow in injector plate 23 occurs in thereverse direction, since annular gap 45 is designed with a smallerdiameter than outlet orifice 42 and thus smaller than inlet areas 47 inswirl-promoting depressions 40. In order to achieve the radial offset ofinlet and outlet of injector plate 23, it is recommended that anadditional thin, for example circular, cover disk 50 be provided oninjector plate 23 on its upper face. This cover disk 50 has such anouter diameter that swirl-promoting depressions 40 are not fully coveredon the outside and thus inlet areas 47 have the desired size. Outletorifice 42 of valve seat body 16, where cover disk 50 is now located,has a larger diameter now than the effective diameter through the outeredge areas of swirl-promoting depressions 40.

Additional examples of embodiment, not illustrated, result from fullyomitting a cover of swirl-promoting depressions 40 or by using coversconfigured differently. Thus it is conceivable to form additional layerssimilar to cover disk 50 directly on injector plate 23 during itsmanufacture, which then perform the function of the cover.

A particularly suitable and preferred manufacturing process for injectorplate 23 is briefly described below. The process is based on a flat andstable substrate, which may consist, for example, of silicon, glass, orceramic. The usual thicknesses of these substrate plates are between 0.5mm and 2 mm. After cleaning the substrate, an auxiliary layer is appliedelectrically on the substrate. This can be an electrical primer layer,(e.g., Cu), necessary to provide conductance for subsequentelectroplating. This auxiliary layer can also serve as a stop layer forthe subsequent microstructuring or as a sacrifice layer to make itpossible to subsequently decollate injector plates 23 in a simplemanner, e.g., by etching. Then a microstructurable layer is applied onthe entire auxiliary layer. A thermoplastically deformable plastic (e.g.polymethylmethacrylate PMMA) is especially advantageously applied to theauxiliary layer, particularly by lamination as a film.

Subsequently this layer is structured using a mask. Microstructuring canbe performed by diamond machining or ablation using excimer laser,especially due to its high precision. The excimer laser used, forexample, for microstructuring, is distinguished by its very high powerdensity and short wavelength (typically λ=193 nm) After this process, anelectroplating mask remains in the PMMA layer. Metal is applied aroundthis mask in an electroplating bath. The metal is applied as aclose-fitting layer on the contour of the electroplating mask, so thatit accurately reproduces the predefined contours. Ni, NiCo, NiFe, or Cuare normally used for electroplating.

Depending on the desired design of injector plate 23, themicrostructuring and electroforming steps can now be repeated. Aftercompleting the electroplating processes, the electroplating masks areremoved. When PMMA is used for the layers to be structured, ethylacetate is especially well-suited for removing it. After this removal,injector plate 23 is on the substrate already in its final form. Finallyinjector plate 23 is decollated. For this purpose, the auxiliary layersare removed by etching and injector plate 23 is lifted off thesubstrate.

Another, very similar manufacturing principle provides for themanufacture of forming tools according to the MIGA method in theabove-described manner, which are exactly the reverse (negativestructure) of the desired injector plate 23. This method is especiallycost-effective for large quantities of injector plates 23.

These forming tools configured as negatives of injector plates 23 mustbe machined so precisely as to be usable at least 10,000 times withunchanged quality. To this end UV intaglio lithography is alsowell-suited for producing injector plate 23. Also in this process, anauxiliary layer (sacrifice layer, electroplating primer layer) isapplied, on which a photoresist is laminated, splashed or sprayed. Thestructure to be produced is than transferred with the help of aphotolithographic mask (UV exposure). After developing the UV-exposedphotoresist, a structure defined by the mask is obtained in thephotoresist, which represents a negative structure of the injector plate23 layer to be obtained later. The remaining photoresist structure issubsequently electrically filled with metal. The process steps afterelectroplating, such as removal of the auxiliary layers and decollatinginjector plate 23 from the substrate take place as in the previouslydescribed method.

What is claimed is:
 1. A fuel injection valve, comprising:a valve needlehaving a longitudinal valve axis; a valve seat surface disposeddownstream of the valve needle; a valve closing element having at leasta first position and a second position, the valve closing elementcooperating with the valve seat surface to control a fuel stream flowingthrough the valve needle; and an injector plate disposed downstream ofthe valve seat surface, the injector plate having an upstream side and adownstream side and having a plurality of swirl-producing depressions onthe upstream side, each of the plurality of swirl-producing depressionshaving a fuel intake area, the injector plate also having at least oneuninterrupted annular gap on the downstream side forming a spraygeometry, the plurality of swirl-producing depressions and the annulargap being connected to allow the fuel stream to flow through theinjector plate.
 2. The device according to claim 1, wherein a width ofthe annular gap is within a range of 25 μm to 50 μm.
 3. The deviceaccording to claim 1, wherein at least a portion of the plurality ofswirl-producing depressions have a rectangular cross section.
 4. Thedevice according to claim 1, wherein the plurality of swirl-producingdepressions are arranged in a circular shape on the injector plate andrun in a turbine vane-like manner in a top view of the injector plate.5. The device according to claim 4, wherein the turbine vane-likearrangement of the swirl-producing depressions is obtained by each ofthe plurality of depressions running substantially in a radial directionand being tilted in a circumferential direction, each of the pluralityof swirl-producing depressions being arranged one behind the other in acircular shape.
 6. The device according to claim 1, wherein the fuelintake areas are arranged in a circular shape, the circular shape havinga diameter less than a diameter of the annular gap, so that a radialoffset exists between the fuel intake areas and the annular gap.
 7. Thedevice according to claim 1, wherein the injector plate is producedusing a microstructuring process in combination with an electroformingprocess.
 8. The device according to claim 7, wherein themicrostructuring process includes diamond machining.
 9. The deviceaccording to claim 7, wherein the microstructuring process includesablation using an excimer laser.
 10. The device according to claim 7,wherein the microstructuring process includes a UV intaglio lithographyprocess.